Conventional serpentine fin machines make strips of fins by infeeding a flat sheet of metallic strip stock and outputting a series of metallic strips having corrugations therein. There are many uses for corrugate fin strips, particularly for vehicle components such as radiator, heater core, evaporator, and condenser fins, among others. The proper fin height is important for these components to allow for proper fin to tube brazing.
The typical fin machine generally works by feeding the continuous length of strip stock between at least one pair of form rollers having interleaved teeth to bend the strip and form corrugations (fins) in the stock. Two significant considerations, as they pertain to the shape of the corrugations, are the average height of the corrugations in a given length of fin stock and the typical variation in fin height from any one given fin to its adjacent fins (fin-to-fin variation). These two considerations are important to optimize the functioning of these fins when installed in the finished assembly.
The average height is generally determined by two main factors. The first factor is the shape of the form rollers and the spacing between the rollers, which determines the coarse average height of the fins. The second factor is the amount of tension imposed on the strip stock as it is fed into the form roller, which determines the fine average height adjustment of the fins.
For these typical machines, periodic samples of the finished fins exiting the fin machine are taken by an operator and measured on a hand device to determine the average height, and this height is compared to the desired nominal height. If the operator determines that the average height is outside of a predetermined limit, he must manually adjust the average tension on the strip stock being fed into the machine and start the hand measuring process over again. This can be particularly difficult given that the adjustment may be in the 1/100's of an inch in height change. If the average height is off, by the time an operator discovers this and corrects it, a significant amount of corrugated fins may be made that must be scrapped. The concern is with measuring and correcting the average height of fin currently coming out of the machine on a continual basis without any substantial time lag for feedback.
In order to more quickly determine the average fin height, attempts have been made to electronically measure the height of the fins as they exit the machine. One such example is disclosed in U.S. Pat. No. 4,753,096 to Wallis ('096). In the '096 patent, an optical sensor, connected to an electronic circuit, is employed along with a measurement shoe, which rests on the finished corrugated fins, to measure the fin height as the fin material exits the machine. However, this measurement has not proven to be accurate enough to properly control the average fin height to within an acceptable range. A problem is that the machine is measuring the fin at the released stage of the operation. In the released state, the fin is generally not stable enough to have a contact measurement taken accurately, i.e., the fin can be compressed by the weight of the device. This is particularly true with thin gauge strip stock and fins that are not formed with tightly packed corrugations. It is desirable to use thinner strip stock, such as 0.003" thick aluminum, because thinner material, when used in applications such as vehicle condensers, allows for less weight on the vehicle and lower material costs.
Furthermore, it is desirable to employ a cheaper sensor than the optical distance sensor that is used in the '096 patent to minimize the contact during measurement, while still maintaining the accuracy required to detect height changes on the order of several ten thousandths of an inch.
Another example of a system, which attempts to measure the average height and provide feedback, is disclosed in Japanese published application 3-243222 ('222). The '222 application employs a shoe which pushes down on the fins with a predetermined amount of force and uses a distance sensor to measure changes in height. However, again the fins can flex during this operation, making accurate measurement still difficult for thin gauge strip stock and fins that are not formed with tightly packed corrugations, and the pressure at which the shoe is pushed down critical.
Thus, it is desirable to have a fin forming machine which allows for accurate and easily adjustable average fine height adjustment as the fins are produced, allowing for immediate corrections in height when necessary.